Claude/windows install compatibility tr di s (#3)

* Fix Windows PowerShell 5.1 compatibility in installer

Use $env:PROCESSOR_ARCHITECTURE for arch detection instead of
RuntimeInformation::OSArchitecture which may not be loaded in
every Windows PowerShell 5.1 session. Also fix null-reference
when user PATH environment variable is empty.

https://claude.ai/code/session_01VFiRDM2ZweyacXN5JneVoP

* Fix executable resolution and tar extraction on Windows

resolveExecutable() used `sh -lc "command -v ..."` which doesn't work
on Windows (no sh). Now uses `cmd /c where` on win32. Also make tar
workspace restoration tolerate symlink failures on Windows — .bin/
symlinks can't be created without Developer Mode, but the actual
package directories are extracted fine.

https://claude.ai/code/session_01VFiRDM2ZweyacXN5JneVoP

* Broad Windows compatibility fixes across the codebase

- runtime.ts: Use path.delimiter instead of hardcoded ":" for PATH
  construction — was completely broken on Windows
- executables.ts: Add Windows fallback paths for Chrome, Edge, Brave,
  and Pandoc in Program Files; skip macOS-only paths on win32
- node-version.ts, check-node-version.mjs, bin/feynman.js: Show
  Windows-appropriate install instructions (irm | iex, nodejs.org)
  instead of nvm/curl on win32
- preview.ts: Support winget for pandoc auto-install on Windows, and
  apt on Linux (was macOS/brew only)
- launch.ts: Catch unsupported signal errors on Windows
- README.md: Add Windows PowerShell commands alongside macOS/Linux
  for all install instructions

https://claude.ai/code/session_01VFiRDM2ZweyacXN5JneVoP

* fix: complete windows bootstrap hardening

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Advait Paliwal <advaitspaliwal@gmail.com>

src/setup/preview.ts

@@ -13,13 +13,35 @@ export function setupPreviewDependencies(): PreviewSetupResult {
 		return { status: "ready", message: `pandoc already installed at ${pandocPath}` };
 	}
 
-	const brewPath = resolveExecutable("brew", BREW_FALLBACK_PATHS);
-	if (process.platform === "darwin" && brewPath) {
-		const result = spawnSync(brewPath, ["install", "pandoc"], { stdio: "inherit" });
-		if (result.status !== 0) {
-			throw new Error("Failed to install pandoc via Homebrew.");
+	if (process.platform === "darwin") {
+		const brewPath = resolveExecutable("brew", BREW_FALLBACK_PATHS);
+		if (brewPath) {
+			const result = spawnSync(brewPath, ["install", "pandoc"], { stdio: "inherit" });
+			if (result.status !== 0) {
+				throw new Error("Failed to install pandoc via Homebrew.");
+			}
+			return { status: "installed", message: "Preview dependency installed: pandoc" };
+		}
+	}
+
+	if (process.platform === "win32") {
+		const wingetPath = resolveExecutable("winget");
+		if (wingetPath) {
+			const result = spawnSync(wingetPath, ["install", "--id", "JohnMacFarlane.Pandoc", "-e"], { stdio: "inherit" });
+			if (result.status === 0) {
+				return { status: "installed", message: "Preview dependency installed: pandoc (via winget)" };
+			}
+		}
+	}
+
+	if (process.platform === "linux") {
+		const aptPath = resolveExecutable("apt-get");
+		if (aptPath) {
+			const result = spawnSync(aptPath, ["install", "-y", "pandoc"], { stdio: "inherit" });
+			if (result.status === 0) {
+				return { status: "installed", message: "Preview dependency installed: pandoc (via apt)" };
+			}
 		}
-		return { status: "installed", message: "Preview dependency installed: pandoc" };
 	}
 
 	return {